diff --git a/yarp/yarp.c b/yarp/yarp.c
index 2573663f26..dd27c172f4 100644
--- a/yarp/yarp.c
+++ b/yarp/yarp.c
@@ -5307,11 +5307,15 @@ lex_question_mark(yp_parser_t *parser) {
         return YP_TOKEN_CHARACTER_LITERAL;
     } else {
         size_t encoding_width = parser->encoding.char_width(parser->current.end);
+
         // We only want to return a character literal if there's exactly one
         // alphanumeric character right after the `?`
         if (
             !parser->encoding.alnum_char(parser->current.end) ||
-            !parser->encoding.alnum_char(parser->current.end + encoding_width)
+            (
+                (parser->current.end + encoding_width >= parser->end) ||
+                !parser->encoding.alnum_char(parser->current.end + encoding_width)
+            )
         ) {
             lex_state_set(parser, YP_LEX_STATE_END);
             parser->current.end += encoding_width;